Currently, one of the challenges of integrated circuit design and manufacturing is to reduce resistive capacitive delay during signal transmission. One solution is to replace an aluminum layer with a copper layer to lower the serial metal resistance. Another solution is to form low-k porous films or air gaps between the metal layers to reduce the parasitic capacitance.
FIG. 1 shows a conventional method for fabricating an interconnect structure. The fabrication method includes: providing a substrate 5 and forming semiconductor devices on the substrate 5; depositing a low-k film 4 on the substrate 5; forming a mask 6 on the low-k film 4; patterning the low-k film 4 using the mask 6 to create through-holes (not illustrated); and filling the through-holes with metal to create an interconnect structure connecting to the semiconductor devices. Specifically, the low-k film 4 is porous and the mask 6 is a hard mask.
In practice, however, conventional interconnect structures often have bump defects. Such bump defects may lower production yield of the interconnect structures and may affect electric connection of the interconnect structures.